内回热器对低温有机朗肯循环热力性能的影响及工质选择

摘要

Most studies on the comparison of organic Rankine cycle(ORC)without internal heat exchanger(IHE)and ORC with internal heat exchanger(IORC)mainly focused on thermal performance changes with the initial parameters,but researches on the comparison based on heat absorption amount are rare. This paper established two systems,ORC without IHE and IORC,with the flue gas as the heat source. Based on the heat absorption amount change with changing the parameter of heat source,the regularity of changes of inlet temperature,net work,heat consumption and exergy loss in the two systems mentioned were analyzed with ten selected fluids,and the better working fluids and their compatibilities with internal heat exchanger showed up. The results showed that when the heat source enters the system at 150℃ and exits between 70℃ to 90℃,plus the pinch temperature keeps at 10℃,IORC is more suitable for the low heat absorption amount area;in the high area,IORC increases little in the thermodynamic performance,and sometimes IORC performs even worse than non-IHE ORC;Through comprehensive comparison,R236ea and R600a are the best choices,and R245fa and R600 are relatively suitable fluids;The difference of thermodynamic performance between the two systems using R123 as working fluid is little,the maximum difference of the heat consumption and net work between IORC and ORC system is only about 600kJ/kg and 2kW,and R123 have worse thermal compatibility with internal heat exchanger.%目前对有机朗肯循环（ORC）有无内回热器的对比研究主要集中在循环热力性能随初参数变化的对比，但很少考虑吸热量对两个系统热力性能的影响。本文以烟气余热为热源，构建无回热和带有内回热的ORC系统，选用10种干工质，通过热源参数变化引起工质吸热量的变化，分析工质分别在两种系统中的初温、净功量、热耗率及㶲损的变化规律，得出了较优工质和各工质对内回热器的匹配性。结果表明：当热源温度为150℃、排烟温度在70～90℃间引起的工质吸热量变化时，在窄点温差为10℃下，带有内回热器的 ORC 系统更适用于吸热量较低的区间；当吸热量较高时，内回热器对系统热力性能提升的能力降低，甚至低于无回热的ORC系统；经综合比较，工质R236ea和R600a最优，工质R245fa和 R600为较适合工质；以R123为工质的带有内回热器和无回热的ORC系统热力性能差异较小，热耗率最大差值仅为约600kJ/kg，净功量最大差值也仅为约2kW，因此， R123对内回热器的热匹配性相对较差。